Accoustic processing device

ABSTRACT

To realize virtual surround reproduction with small deterioration in the SN ratio of an entire reproduction system, in the case of adding together virtual surround signals and front-channel audio signals in an adder  1300,  volume normalization is carried out in a volume normalizing section  1200  before the addition. In the case where the addition is not performed, the virtual surround signals and the front-channel audio signals are output independently of each other without being subjected to volume normalization in the volume normalizing section  1200.

TECHNICAL FIELD

The present invention relates to an audio processor which realizesmultichannel reproduction in a virtual manner only with frontloudspeakers placed in front of a listener.

BACKGROUND ART

With the advent of the sound sources compliant with multichannel audioreproduction, such as DVD (Digital Versatile Disc), BS digitalbroadcasting, etc., in order to allow a user who has only a 2-channelloudspeaker system to enjoy multichannel reproduction, various audioprocessors which realizes multichannel reproduction in a virtual manneronly with front loudspeakers have been developed. Specifically, in suchan audio processor, to reproduce audio signals for rear channels throughloudspeakers placed in front of a listener, the audio signals aresubjected to sound image localization such that the sound image positionwhich is perceived by the listener is at the rear of the listener(virtual surround processing).

A known example of such an audio processor is an audio processor 4000which adds together signals obtained by performing the virtual surroundprocessing on rear-channel audio signals (virtual surround signals) andfront-channel audio signals to output audio PCM signals for the frontloudspeakers as shown in FIG. 12 (see Patent Document 1 and PatentDocument 2).

The audio processor 4000 includes a virtual surround processing section4100, a volume normalizing section 4200, and an adder 4300.

Among externally-input audio PCM signals of 4 channels in total, i.e.,front-channel audio signals for front left and right reproduction (2channels for left and right) and rear-channel audio signals for rearleft and right reproduction (2 channels for left and right), the virtualsurround processing section 4100 performs the virtual surroundprocessing on the rear-channel audio signals to output virtual surroundsignals.

The volume normalizing section 4200 performs a process on thefront-channel audio signals and the virtual surround signals such thatthe volume levels of the signals are within a predetermine level range(volume normalization). The volume normalization is performed for thepurpose of preventing occurrence of an overflow in the addition of thefront-channel audio signals and the virtual surround signals.

The adder 4300 adds together the front-channel audio signals and thevirtual surround signals which have been volume-normalized by the volumenormalizing section 4200.

When front-channel audio signals and rear-channel audio signals areinput from the outside of the thus-constructed audio processor 4000, thevirtual surround processing section 4100 performs the virtual surroundprocessing on the front-channel audio signals to output virtual surroundsignals to the volume normalizing section 4200. After the volumenormalizing section 4200 performs the volume normalization on thefront-channel audio signals and the virtual surround signals, thesenormalized signals are added together by the adder 4300 and output asaudio PCM signals for front loudspeakers.

As described above, in the audio processor 4000, the virtual surroundprocessing is performed on rear-channel audio signals, wherebymultichannel reproduction is realized in a virtual manner only withfront loudspeakers.

Another example of an audio processor which realizes multichannelreproduction in a virtual manner is an audio processor 5000 whereinreflection sound creation processing which creates reflection sound in avirtual manner is performed on 2-channel audio PCM signals for frontleft and right reproduction (2-channel stereo audio signals) which areinput from the outside of the audio processor to generate pseudorear-channel audio signals (see, for example, Patent Document 3).

The audio processor 5000 includes a virtual surround processing section4100, a volume normalizing section 4200, an adder 4300, and a reflectionsound processing section 5400.

The reflection sound processing section 5400 performs a process whichcreates reflection sound in a virtual manner (reflection sound creationprocessing) on 2-channel stereo audio signals to output rear-channelaudio signals.

In the thus-constructed audio processor 5000, the reflection soundprocessing section 5400 performs the reflection sound creationprocessing on 2-channel stereo audio signals to output pseudorear-channel audio signals. These rear-channel audio signals aresubjected to the virtual surround processing in the virtual surroundprocessing section 4100. The virtual surround-processed signals and thestereo audio signals of the channels are subjected to volumenormalization in the volume normalizing section 4200 and added togetherat the adder 4300.

That is, in the audio processor 5000, 2-channel stereo audio signals aresubjected to sound image expansion processing and added to the originalsignals, whereby multichannel reproduction that achieves a stereophoniceffect in a virtual manner is realized.

[Patent Document 1] Japanese Laid-Open Patent Publication No. 6-233394

[Patent Document 2] Japanese Laid-Open Patent Publication No. 10-174197

[Patent Document 3] Japanese Laid-Open Patent Publication No. 8-116597

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

A trend in audio processors (or video/audio processors which alsoprocess video signals) targeting the systems which have been rapidlypropagating in recent years, such as DVD and the like, exhibits higherperformance and higher sound quality which are demanded in considerationof hi-fi users as targets. However, when virtual surround signals andfront-channel audio signals are added together, the SN ratio can bedeteriorated due to normalization which is performed for avoiding anoverflow during the addition.

In an audio processor in which the presence/absence (ON/OFF) of thevirtual surround processing can be switched, the play volume isdecreased by volume normalization not only when the virtual surroundprocessing is ON but also when the virtual surround processing is OFF inorder to adjust the sound voluminosity between ON and OFF of the virtualsurround processing. As a result, the SN ratio of the entire system isdeteriorated.

When rear loudspeakers are inevitably placed in front of a listener foruser's convenience even with a multichannel-reproducible system,reproduction has to be carried out with the output of the rearloudspeakers being OFF. As a result, as in a 2-channel reproductionsystem, the SN ratio is deteriorated by normalization which is performedfor avoiding an overflow.

The present invention was conceived in view of the above problems. Anobjective of the present invention is to provide an audio processorcapable of virtual surround reproduction with small deterioration in theSN ratio of the entire reproduction system.

Means for Solving the Problems

In order to achieve the above objective, the invention of claim 1 is anaudio processor which comprises an audio processing section forperforming a predetermined sound image localization process on arear-channel audio signal whose sound image position perceived by alistener when reproduced through a loudspeaker placed at the rear of thelistener is at the rear of the listener such that the sound imageposition perceived by the listener when the signal is reproduced througha loudspeaker placed in front of the listener is at the rear of thelistener to generate a sound image localized audio signal, wherein afront-channel audio signal whose sound image position perceived by thelistener when reproduced through the loudspeaker placed in front of thelistener is in front of the listener and the sound image localized audiosignal are output independently of each other.

The invention of claim 2 is based on the audio processor of claim 1 andfurther comprises a reflection sound creation section for performing areflection sound creation process on an input front-channel audio signalto generate the rear-channel audio signal.

The invention of claim 3 is based on the audio processor of claim 1 andfurther comprises a reflection sound adding section for adding areflection sound signal to each of an input front-channel audio signaland an input rear-channel audio signal to generate the front-channelaudio signal and the rear-channel audio signal.

With these inventions, the front-channel audio signal and the soundimage localized audio signal are output independently of each other.Thus, in the case where the front-channel audio signal and the soundimage localized audio signal are added together in an external analogcircuit, virtual surround reproduction is enabled without deteriorationin the SN ratio.

The invention of claim 4 is based on the audio processor of claim 1 andfurther comprises: a volume normalizing section for controlling thevolume level of the front-channel audio signal and the sound imagelocalized audio signal to be within a predetermined level range; anadder for adding together the front-channel audio signal whose volumelevel has been controlled in the volume normalizing section and thesound image localized audio signal whose volume level has beencontrolled in the volume normalizing section to generate a sum audiosignal; and a switching section for selectively performing an operationof outputting the front-channel audio signal and the sound imagelocalized audio signal independently of each other and an operation ofoutputting the sum audio signal according to a control signal indicativeof output control information.

With this invention, the output operation is switched according to aninput control signal.

The invention of claim 5 is based on the audio processor of claim 4,wherein: the output control information includes output channel typeinformation which is indicative of an output channel type; and theswitching section performs the switching according to the output channeltype information.

With this invention, the output operation is switched according to theoutput channel type.

The invention of claim 6 is based on the audio processor of claim 5 andfurther comprises a volume controller for controlling the volume levelof an output audio signal according to the output channel typeinformation and an input volume level.

With this invention, the level of an output audio signal is controlledaccording to the output channel type, and optimum volume control isrealized.

The invention of claim 7 is based on the audio processor of claim 4,wherein: the output control information includes rear loudspeaker layoutinformation indicative of whether a layout of a loudspeaker for rearsound image through which an audio signal is output such that a soundimage position perceived by a listener is at the rear of the listener isa layout where the loudspeaker is placed in front of the listener, alayout where the loudspeaker is placed at the rear of the listener, or alayout where the loudspeaker is not provided; the audio processingsection controls whether or not to generate the sound image localizedaudio signal according to the layout indicated by the rear loudspeakerlayout information; and the switching section selectively performsaccording to the rear loudspeaker layout information an operation ofoutputting the front-channel audio signal and the sound image localizedaudio signal independently of each other, an operation of outputting thesum audio signal, and an operation of outputting an input audio signalas it is.

With this invention, the presence/absence of sound image localization orthe output operation is switched according to the layout of loudspeakersthrough which output is realized.

The invention of claim 8 is based on the audio processor of claim 7 andfurther comprises a volume controller for controlling the volume levelof an output audio signal according to the rear loudspeaker layoutinformation and an input volume level.

With this invention, the level of an output audio signal is controlledaccording to the layout of loudspeakers through which output isrealized.

Effects of the Invention

According to the present invention, virtual surround reproduction can berealized with small deterioration in the SN ratio of an entirereproduction system.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a structure of an audio processoraccording to embodiment 1 of the present invention.

FIG. 1 is a flowchart illustrating an operation of the audio processoraccording to embodiment 1 of the present invention.

FIG. 3 is a block diagram showing a structure of an audio processoraccording to embodiment 2 of the present invention.

FIG. 4 is a flowchart illustrating an operation of the audio processoraccording to embodiment 2 of the present invention.

FIG. 5 is a block diagram showing a structure of an audio processoraccording to embodiment 3 of the present invention.

FIG. 6 shows an example of a structure of a reproduction system whichincorporates the audio processor according to embodiment 3 of thepresent invention.

FIG. 7 shows an example of a structure of a reproduction system whichincorporates the audio processor according to embodiment 3 of thepresent invention.

FIG. 8 shows an example of a structure of a reproduction system whichincorporates the audio processor according to embodiment 3 of thepresent invention.

FIG. 9 shows an example of a structure of a reproduction system whichincorporates the audio processor according to embodiment 3 of thepresent invention.

FIG. 10 is a table which shows the operation status of processingsections for rear loudspeaker layout information in the audio processoraccording to embodiment 3 of the present invention.

FIG. 11 is a flowchart illustrating an operation of the audio processoraccording to embodiment 3 of the present invention.

FIG. 12 is a block diagram showing a structure of a conventional audioprocessor.

FIG. 13 is a block diagram showing a structure of a conventional audioprocessor.

DESCRIPTION OF THE REFERENCE NUMERALS

1000 Audio processor

1100 Virtual surround processing section

1200 Volume normalizing section

1300 Adder

1400 Output switching section

1500 External interface

1700 Automatic volume controller

2000 Audio processor

2500 External interface

2600 Reflection sound processing section

2700 Automatic volume controller

3000 Audio processor

3100 Virtual surround processing section

3200 Volume normalizing section

3400 Output switching section

3500 External interface

3600 Reflection sound processing section

3700 Automatic volume controller

4000 Audio processor

4100 Virtual surround processing section

4200 Volume normalizing section

4300 Adder

5000 Audio processor

5400 Reflection sound processing section

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described withreference to the drawings.

Embodiment 1

FIG. 1 is a block diagram showing a structure of an audio processor 1000according to embodiment 1 of the present invention. As shown in FIG. 1,the audio processor 1000 includes a virtual surround processing section1100, a volume normalizing section 1200, an adder 1300, an outputswitching section 1400, and an external interface 1500.

Specifically, the audio processor 1000 is formed by a DSP (DigitalSignal Processor), or the like, and performs a predetermined process onexternally-input audio PCM signals of 4 channels in total, i.e.,front-channel audio signals for front left and right reproduction andrear-channel audio signals for rear left and right reproduction, toperforms the following two types of output operations.

The output operation of the first type is such that, in order toreproduce audio signals for rear channels through loudspeakers placed infront of a listener, the rear-channel audio signals are subjected tosound image localization such that the sound image position perceived bythe listener is at the rear of the listener (virtual surroundprocessing), the processed audio signals are added to the rear-channelaudio signals, and the resultant signals are output as 2-channel signalsfor front loudspeakers. With the output signals, multichannelreproduction can be realized in a virtual manner only with the frontloudspeakers (virtual surround reproduction).

The output operation of the second type is the operation of outputtingsignals of 4 channels, i.e., the front-channel audio signals and thevirtual surround processed signals (virtual surround signals). Forexample, where the output front-channel signals and the virtual surroundsignals are added together in an external analog circuit, and theresultant signals are output through the front loudspeakers, or wherethe rear loudspeakers are placed in front of a listener for user'sconvenience, if the virtual surround signals are output through the rearloudspeakers placed in front of the listener, virtual surroundreproduction is realized also in this case.

Selection of the output operation type is controlled based on the outputcontrol information (described later) which is input from the outside ofthe audio processor 1000.

In embodiment 1, this output control information is output channel typeinformation indicative of whether or not the output format is 2-channeloutput format where the channel type of audio PCM signals output to theoutside is 2-channel format or 4-channel output format where the channeltype of audio PCM signals output to the outside is 4-channel format.

The virtual surround processing section 1100 performs the virtualsurround processing on the rear-channel audio signals to output thevirtual surround signals.

When the output channel type information indicates 2-channel outputformat, the volume normalizing section 1200 performs volumenormalization such that the volume of the front-channel audio signalsand the virtual surround signals is decreased by 6 dB. When the outputchannel type information indicates 4-channel output format, the volumenormalizing section 1200 simply passes the front-channel audio signalsand the virtual surround signals therethrough. The reason why the volumenormalization is performed in the case of 2-channel output format is inorder to prevent occurrence of an overflow in the addition of thefront-channel audio signals and the virtual surround signals.

The adder 1300 adds together the front-channel audio signals which havebeen subjected to the volume normalization in the volume normalizingsection 1200 and the virtual surround signals output from the outputswitching section 1400.

When the output channel type information indicates 2-channel outputformat, the output switching section 1400 outputs to the adder 1300 thevirtual surround signals output from the volume normalizing section1200. When the output channel type information indicates 4-channeloutput format, the output switching section 1400 outputs signals for therear loudspeakers to the outside of the audio processor 1000.

The external interface 1500 outputs the externally-input output controlinformation to the volume normalizing section 1200 and the outputswitching section 1400.

The audio processor 1000 as constructed above performs any of 4-channeloutput or 2-channel output according to the output control informationthrough the processes of the steps illustrated in the flowchart of FIG.2. At the respective steps, the following processes are performed.

Audio PCM signals of 4 channels in total, i.e., front-channel audiosignals and rear-channel audio signals, are input to the virtualsurround processing section 1100.

The virtual surround processing section 1100 performs the virtualsurround processing on the rear channel audio signals to output theresultant signals as virtual surround signals to the volume normalizingsection 1200.

The volume normalizing section 1200 determines whether the outputchannel type information output from the external interface 1500indicates 2-channel output format or 4-channel output format in order todetermine whether or not the volume normalization of the audio signalsis necessary. In the case of 2-channel output format, the operationproceeds to the process of step S104. In the case of 4-channel outputformat, the volume normalizing section 1200 simply passes thefront-channel audio signals and the virtual surround signalstherethrough, and then, the operation proceeds to the process of stepS105.

The volume normalizing section 1200 performs the volume normalization onthe front-channel audio signals and the virtual surround signals.Specifically, the volume of these signals is decreased by 6 dB.

With this, occurrence of an overflow is prevented in the addition of thefront-channel audio signals and the virtual surround signals.

The output switching section 1400 determines whether the output channeltype information indicates 2-channel output format or 4-channel outputformat in order to determine to which section the virtual surroundsignals are to be output. In the case of 2-channel output format, theoutput switching section 1400 outputs the virtual surround signals tothe adder 1300, and then, the operation proceeds to the process of stepS106. In the case of 4-channel output format, the operation proceeds tothe process of step S107.

The adder 1300 adds together the front-channel audio signals and thevirtual surround signals, and then, the operation proceeds to theprocess of step S107.

The output of the adder 1300 is output as signals for the frontloudspeakers while the output of the output switching section 1400 isoutput as signals for the rear loudspeakers.

By performing the processes of steps S101 through S107, any of 4-channeloutput and 2-channel output is performed according to the output controlinformation.

For example, when the output channel type information indicates2-channel output format (the output channel type is 2-channel output),the virtual surround processing section 1100 performs the virtualsurround processing on the rear-channel audio signals to generatevirtual surround signals. The volume of this virtual surround signals isdecreased by 6 dB in the volume normalizing section 1200. Thereafter,the resultant virtual surround signals are output to the adder 1300through the output switching section 1400. The adder 1300 adds togetherthe virtual surround signals and the front-channel audio signals tooutput the resultant signals as signals for the front loudspeakers. Inthe process of addition, an overflow due to the addition process doesnot occur because the audio signals have been subjected to normalizationin the volume normalizing section 1200.

When the output channel type information indicates 4-channel outputformat (the output channel type is 4-channel output), the virtualsurround signals are generated as in the example of 2-channel outputformat. Thereafter, the front-channel audio signals are output assignals for the front loudspeakers, and the virtual surround signals areoutput as signals for the rear loudspeakers, without being subjected tothe volume normalization in the volume normalizing section 1200 or theaddition in the adder 1300. Herein, although the normalization is notperformed on the audio signals in the volume normalizing section 1200,it is natural that no overflow occurs because the addition is notperformed.

As described above, according to this embodiment, since the outputswitching section 1400 is provided, the virtual surround signals and thefront-channel audio signals can be independently output without beingadded together. For example, in the case where front-channel signals andvirtual surround signals are added together in an external analogcircuit, virtual surround reproduction can be realized with a 2-channelloudspeaker system without deteriorating the SN ratio of an entirereproduction system.

With externally-input output channel type information, thepresence/absence of volume normalization and the presence/absence ofaddition of the virtual surround signals and the front-channel audiosignals are automatically switched according to an external outputchannel type. Thus, the volume is optimally set according to the form ofa reproduction system, and as a result, the SN ratio of the entirereproduction system is automatically optimized.

Embodiment 2

An example of a processor described herein is capable of two types ofoutput operations as in the processor of embodiment 1, i.e., 2-channeloutput format and 4-channel output format, although input audio signalsare audio PCM signals of 2 channels for front left and rightreproduction (stereo).

FIG. 3 is a block diagram showing a structure of an audio processor 2000according to embodiment 2 of the present invention. In the followingsections, components that have the same functions as those of embodiment1 are denoted by the same reference numerals, and the descriptionsthereof are herein omitted.

As shown in FIG. 3, the audio processor 2000 includes an externalinterface 2500 in substitution for the external interface 1500 ofembodiment 1 and further includes a reflection sound processing section2600 and an automatic volume controller 2700. The audio processor 2000selects any of 2-channel output format and 4-channel output format basedon the output control information. Specifically, the audio processor2000 is also formed by a DSP, or the like.

The external interface 2500 outputs the above-described output channeltype information to the volume normalizing section 1200, the outputswitching section 1400, and the automatic volume controller 2700.

The reflection sound processing section 2600 performs onexternally-input stereo audio PCM signals (front-channel audio signals)the process of creating reflection sound in a virtual manner and addingthe created reflection sound to the stereo audio PCM signals (reflectionsound creation processing), thereby generating pseudo rear-channelsignals.

The automatic volume controller 2700 performs volume control accordingto the sound level of input signals only when the output channel typeinformation indicates 2-channel output format. For example, when thevolume level of the input signals is an excessively large level, thevolume level is automatically smoothed or compressed. Although anoverflow is more likely to occur when a plurality of audio signals areadded together, the overflow state can be relaxed by automatic volumecontrol of the automatic volume controller 2700.

In embodiment 2, the volume normalizing section 1200 decreases the levelof the input signals by 3 dB, while in embodiment 1 the volumenormalizing section 1200 decreases the level of the input signals by 6dB. The reason why the decrease in signal level by the volumenormalizing section 1200 is 3 dB in embodiment 2 is that the audioprocessor 2000 includes the automatic volume controller 2700, andaccordingly, some degree of overflow can be avoided.

The audio processor 2000 as constructed above performs any of 4-channeloutput or 2-channel output according to the output control informationthrough the processes of the steps illustrated in the flowchart of FIG.4. At the respective steps, the following processes are performed.

Audio PCM signals are input to the virtual surround processing section1100 and the reflection sound processing section 2600.

The reflection sound processing section 2600 performs the reflectionsound creation processing on front-channel audio signals to generatepseudo rear-channel audio signals.

The virtual surround processing section 1100 performs the virtualsurround processing on the pseudo rear channel audio signals to outputthe resultant signals as virtual surround signals to the volumenormalizing section 1200.

The volume normalizing section 1200 determines whether the outputchannel type information output from the external interface 2500indicates 2-channel output format or 4-channel output format in order todetermine whether or not the volume normalization of the audio signalsis necessary. In the case of 2-channel output format, the operationproceeds to the process of step S205. In the case of 4-channel outputformat, the volume normalizing section 1200 simply passes thefront-channel audio signals and the virtual surround signalstherethrough, and then, the operation proceeds to the process of stepS206.

The volume normalizing section 1200 performs the volume normalization onthe front-channel audio signals and the virtual surround signals.Specifically, the volume of these signals is decreased by 3 dB.

With this, occurrence of an overflow is prevented in the addition of thefront-channel audio signals and the virtual surround signals.

The output switching section 1400 determines whether the output channeltype information indicates 2-channel output format or 4-channel outputformat in order to determine to which section the virtual surroundsignals are to be output. In the case of 2-channel output format, theoutput switching section 1400 outputs the virtual surround signals tothe adder 1300, and then, the operation proceeds to the process of stepS106. In the case of 4-channel output format, the operation proceeds tothe process of step S107.

The adder 1300 adds together the front-channel audio signals and thevirtual surround signals, and then, the operation proceeds to theprocess of step S107.

The automatic volume controller 2700 determines whether the outputchannel type information indicates 2-channel output format or 4-channeloutput format in order to determine whether or not the automatic volumecontrol is necessary. In the case of 2-channel output format, theoperation proceeds to the process of step S209 for volume adjustment. Inthe case of 4-channel output format (i.e., when volume adjustment isunnecessary), the operation proceeds to the process of step S210.

The automatic volume controller 2700 adjusts the volume of thefront-channel audio signals and the virtual surround signals bysmoothing or compressing the volume level.

Outputs of the automatic volume controller 2700 are output as signalsfor the front loudspeakers and signals for the rear loudspeakers.

By performing the processes of steps S201 through S210, any of 4-channeloutput and 2-channel output is performed according to the output controlinformation.

For example, when the output channel type information indicates2-channel output format, the reflection sound processing section 2600performs the reflection sound creation processing to generate pseudorear-channel audio signals. The virtual surround processing section 1100performs the virtual surround processing on these rear-channel audiosignals to generate virtual surround signals. The volume of thesevirtual surround signals is decreased by 3 dB in the volume normalizingsection 1200. Thereafter, the resultant virtual surround signals areoutput to the adder 1300 through the output switching section 1400. Theadder 1300 adds together the virtual surround signals and thefront-channel audio signals to output the resultant signals as signalsfor the front loudspeakers. In the process of addition, an overflow dueto the addition process does not occur because the rear-channel audiosignals and the virtual surround signals have been subjected tonormalization in the volume normalizing section 1200. When the volumelevel of the signals output from the adder 1300 is an excessively largelevel, the volume level is automatically smoothed or compressed, wherebythe overflow state can be relaxed. Then, the signals whose volume hasbeen controlled by the automatic volume controller 2700 are output tothe front loudspeaker side.

When the output channel type information indicates 4-channel outputformat, the virtual surround signals are generated as in the example of2-channel output format. Thereafter, the front-channel audio signals areoutput as signals for the front loudspeakers, and the virtual surroundsignals are output as signals for the rear loudspeakers, without beingsubjected to the volume normalization in the volume normalizing section1200, the addition in the adder 1300, or the volume control in theautomatic volume controller 2700. Herein, although none of the volumenormalization in the volume normalizing section 1200 and the automaticvolume control in the automatic volume controller 2700 is performed onthe audio signals, it is natural that no overflow occurs because theaddition is not performed.

As described above, according to this embodiment, pseudo rear-channelsignals are generated from front-channel audio signals, and therefore,even if the input signals are only front-channel audio signals, audiosignals can be output according to the output channel type of areproduction system which incorporates the audio processor of embodiment2 while maintaining the optimum SN ratio of the entire reproductionsystem as in the processor of embodiment 1.

Since the automatic volume controller which adjusts the volume levelaccording to the output channel type information is provided, the volumecontrol process can be switched according to the output channel type,and as a result, an optimum volume control process can be achieved.

Embodiment 3

FIG. 5 is a block diagram showing a structure of an audio processor 3000according to embodiment 3 of the present invention. The audio processor3000 includes an adder 1300, an automatic volume controller 2700, avirtual surround processing section 3100, a volume normalizing section3200, an output switching section 3400, an external interface 3500, areflection sound processing section 3600, and an automatic volumecontroller 3700. The audio processor 3000 outputs audio PCM signalsaccording to the layout of rear loudspeakers.

In this embodiment, the output control information is informationindicative of the layout of rear loudspeakers in a reproduction systemwhich incorporates the audio processor 3000 (rear loudspeaker layoutinformation). The rear loudspeaker layout information indicates any of“rear layout” where the rear loudspeakers are placed at the rear of alistener, “front layout” where the rear loudspeakers are placed in frontof a listener, and “none” where no rear loudspeakers are placed.

“Rear layout” represents the case where rear loudspeakers are placed atthe rear of a listener of a reproduction system as in a normalmultichannel system as shown in FIG. 6.

“Front layout” represents the case where rear loudspeakers are placed infront of a listener as shown in FIG. 7 or the case where a rearloudspeaker output and a front loudspeaker output are added together inan external analog circuit of the audio processor 3000 as shown in FIG.8.

“None” represents the case where virtual surround signals andfront-channel audio signals are added together inside the audioprocessor 3000 to provide front loudspeaker output as shown in FIG. 9.

The virtual surround processing section 3100 receives the rearloudspeaker layout information from the external interface 3500. If therear loudspeaker layout information indicates any of “front layout” and“none”, the virtual surround processing section 3100 performs thevirtual surround processing on the front-channel audio signals to outputvirtual surround signals. If the rear loudspeaker layout informationindicates “rear layout”, the virtual surround processing section 3100passes the front-channel audio signals therethrough without performingthe virtual surround processing.

The external interface 3500 outputs the rear loudspeaker layoutinformation to the virtual surround processing section 3100, the volumenormalizing section 1200, the output switching section 1400 and theautomatic volume controller 2700.

If the rear loudspeaker layout information output from the externalinterface 3500 indicates “none”, the volume normalizing section 3200decreases the level of the front-channel audio signals and the virtualsurround signals generated by the virtual surround processing section3100 by 3 dB. The reason why the decrease in signal level by the volumenormalizing section 3200 in embodiment 3 is not 6 dB as in embodiment 1but 3 dB is that the audio processor 3000 includes the automatic volumecontroller 2700, and accordingly, some degree of overflow can beavoided.

The output switching section 3400 outputs the virtual surround signalsto the adder 1300 only if the rear loudspeaker layout information outputfrom the external interface 3500 indicates “none”. If the rearloudspeaker layout information indicates “front layout” or “rearlayout”, the output switching section 3400 outputs the virtual surroundsignals to the rear loudspeaker output side.

The reflection sound processing section 3600 externally receives audioPCM signals of 4 channels in total, i.e., front-channel audio signalsfor front left and right reproduction and rear-channel audio signals forrear left and right reproduction, and performs the reflection soundcreation processing on the front-channel audio signals and therear-channel audio signals. In this embodiment, reflection sound can beadded to the audio signals of all the channels. Even when rear-channelaudio signals are not input, for example, pseudo rear-channel signalscan be generated by performing the reflection sound creation processingon the front-channel audio signals.

When reflection sound is added to a channel already existing at the timeof input, the reflection sound processing section 3600 performs volumenormalization in advance.

The automatic volume controller 3700 performs volume level control(e.g., smoothing or compression) on input signals according to the rearloudspeaker layout information. Specifically, only if the rearloudspeaker layout information output from the external interface 3500indicates “none”, the volume control is carried out according to thevolume level of the input signals. If the rear loudspeaker layoutinformation indicates “front layout” or “rear layout”, the automaticvolume controller 3700 simply passes the input signals therethrough.With this, for example, when the volume level of input signals is anexcessively large level, the volume level is smoothed or compressed,whereby the overflow state can be relaxed.

FIG. 10 is a table that illustrates the operation of the virtualsurround processing section 3100, the volume normalizing section 3200,the output switching section 3400, and the automatic volume controller3700 for respective rear loudspeaker layouts.

The audio processor 3000 as constructed above performs the outputoperation according to the layout of the rear loudspeakers, i.e., thelayout where the rear loudspeakers are placed at the rear of a listener,the layout where the rear loudspeakers are placed in front of alistener, or the layout where no rear loudspeakers are placed, throughthe processes of the steps illustrated in the flowchart of FIG. 11. Atthe respective steps, the following processes are performed.

Audio PCM signals are input to the reflection sound processing section3600.

The reflection sound processing section 3600 performs the reflectionsound creation processing on front-channel audio signals andrear-channel audio signals to add reflection sound.

The virtual surround processing section 3100 analyzes the rearloudspeaker layout information output from the external interface 3500.If the rear loudspeaker layout information indicates “front layout” or“none”, the operation proceeds to the process of step S304 for thevirtual surround processing. If the rear loudspeaker layout informationindicates “rear layout”, the virtual surround processing section 3100simply passes the rear-channel audio signals therethrough, and theoperation proceeds to the process of step S305.

The virtual surround processing section 3100 performs the virtualsurround processing on the rear-channel audio signals output from thereflection sound processing section 3600 to output virtual surroundsignals to the volume normalizing section 3200.

The volume normalizing section 3200 analyzes the rear loudspeaker layoutinformation output from the external interface 3500. If the rearloudspeaker layout information indicates “none”, the operation proceedsto the process of step S306 for volume normalization. If the rearloudspeaker layout information indicates “front layout” or “rearlayout”, the volume normalizing section 3200 simply passes therear-channel audio signals and the virtual surround signalstherethrough, and the operation proceeds to the process of step S307.

The reflection sound processing section 3600 performs volumenormalization on front-channel audio signals and rear-channel audiosignals. Specifically, the reflection sound processing section 3600decreases the volume of these signals by 3 dB.

With this, occurrence of an overflow is prevented in the addition of thefront-channel audio signals and the virtual surround signals.

The output switching section 3400 analyzes the rear loudspeaker layoutinformation in order to determine to which section the virtual surroundsignals are to be output. If the rear loudspeaker layout informationindicates “none”, the output switching section 3400 outputs the virtualsurround signals to the adder 1300, and then, the operation proceeds tothe process of step S308. If the rear loudspeaker layout informationindicates “front layout” or “rear layout”, the output switching section3400 simply passes the rear-channel audio signals therethrough, and theoperation proceeds to the process of step S309.

The adder 1300 adds together the front-channel audio signals and thevirtual surround signals, and then, the operation proceeds to theprocess of step S309.

The automatic volume controller 3700 analyzes the rear loudspeakerlayout information in order to determine whether or not the automaticvolume control is necessary. If the rear loudspeaker layout informationindicates “none”, the operation proceeds to the process of step S310 forvolume adjustment. If the rear loudspeaker layout information indicates“front layout” or “rear layout” (i.e., if volume adjustment isunnecessary), the operation proceeds to the process of step S311.

The automatic volume controller 3700 adjusts the volume of thefront-channel audio signals and the virtual surround signals bysmoothing or compressing the volume level.

Outputs of the automatic volume controller 3700 are output as signalsfor the front loudspeakers and signals for the rear loudspeakers.

By performing the processes of steps S301 through S311, the outputoperation is performed according to the layout of the rear loudspeakers,i.e., the layout where the rear loudspeakers are placed at the rear of alistener, the layout where the rear loudspeakers are placed in front ofa listener, or the layout where no rear loudspeakers are placed.

For example, in a reproduction system where rear loudspeakers are placedas shown in FIG. 6, if the input rear loudspeaker layout informationindicates “rear layout”, the reflection sound processing section 3600performs volume normalization on input 4-channel audio PCM signals andadds reflection sound. The virtual surround processing section 3100simply passes the rear-channel audio signals output from the reflectionsound processing section 3600 therethrough without performing thevirtual surround processing.

The volume normalizing section 3200 simply passes the front-channelaudio signals output from the reflection sound processing section 3600and the rear-channel audio signals output from the virtual surroundprocessing section 3100 therethrough without performing volumenormalization.

Since the output switching section 3400 outputs the rear-channel audiosignals received from the volume normalizing section 3200 to the adder1300, the front-channel audio signals are independently input to theautomatic volume controller 3700. The automatic volume controller 3700also simply passes the front-channel audio signals and the rear-channelaudio signals, which are then output as signals for the frontloudspeakers and signals for the rear loudspeakers, respectively.

As described above, if the input rear loudspeaker layout informationindicates “rear layout”, input 4-channel audio PCM signals are output tothe outside without being subjected to the volume normalization of thevolume normalizing section 3200 or the automatic volume control of theautomatic volume controller 3700. For example, in a reproduction systemconstructed as shown in FIG. 6, surround reproduction can be realizedwithout deteriorating the SN ratio.

Alternatively, for example, in a reproduction system where loudspeakersare placed as shown in FIG. 7 or FIG. 8, if the input rear loudspeakerlayout information indicates “front layout”, the virtual surroundprocessing section 3100 performs an operation different from thatperformed in the case of “rear layout”. Specifically, the virtualsurround processing section 3100 performs the virtual surroundprocessing on the rear-channel audio signals output from the reflectionsound processing section 3600 to generate virtual surround signals.

As described above, rear-channel audio signals and virtual surroundsignals are output to the outside without being subjected to the volumenormalization of the volume normalizing section 3200 or the automaticvolume control of the automatic volume controller 3700. For example, ina reproduction system constructed as shown in FIG. 7, front-channelaudio signals are output through front loudspeakers, and virtualsurround signals are output through rear loudspeakers placed in front ofa listener. Thus, virtual surround reproduction can be realized withoutdeteriorating the SN ratio. For example, in a reproduction systemconstructed as shown in FIG. 8, a front loudspeaker output and a rearloudspeaker output are added together in an external analog circuit,whereby virtual surround reproduction can also be realized.

For example, in a reproduction system where loudspeakers are placed asshown in FIG. 9, if the input rear loudspeaker layout informationindicates “none”, the reflection sound processing section 3600 performsvolume normalization on input 4-channel audio PCM signals and addsreflection sound to the signals. The virtual surround processing section3100 performs the virtual surround processing on rear-channel audiosignals generated by the reflection sound processing section 3600 togenerate virtual surround signals.

The volume normalizing section 3200 performs volume normalization on thefront-channel audio signals and the virtual surround signals.Specifically, the volume normalizing section 3200 decreases the volumeof each of these signals by 3 dB.

The output switching section 3400 outputs the virtual surround signalsreceived from the volume normalizing section 3200 to the adder 1300, andthe adder 1300 adds together the front-channel audio signals and thevirtual surround signals. The resultant signals are input to theautomatic volume controller 3700. The automatic volume controller 3700performs volume control on the output of the adder 1300 according to thevolume level of the signals to output the resultant signals for frontloudspeakers. The volume control in the automatic volume controller 3700provides the effect of relaxing the overflow state by automaticallysmoothing or compressing the volume level as in the processor ofembodiment 2 when the volume level of the input signals is anexcessively large level, for example.

In this way, addition is performed after volume normalization of thevolume normalizing section 3200 has been performed, and signals areoutput to the outside after being subjected to automatic volume controlin the automatic volume controller 3700. Therefore, overflow does notoccur in the addition process or at the time of external output. Forexample, virtual surround reproduction can be realized with areproduction system constructed as shown in FIG. 9.

As described above, according to this embodiment, since the outputswitching section 3400 is provided, virtual surround signals and2-channel signals for front reproduction can be independently outputwithout being added together irrespective of the presence/absence(ON/OFF) of the virtual surround processing. Therefore, it is notnecessary to decrease the reproduction volume in the case of OFF inorder to adjust the sound voluminosity between the case where thevirtual surround processing is ON and the case where the virtualsurround processing is OFF. Thus, the SN ratio of the entirereproduction system can be maintained.

With externally-input output channel type information, thepresence/absence of volume normalization in the volume normalizingsection, the presence/absence of volume level adjustment in theautomatic volume controller, and the presence/absence of addition of thevirtual surround signals and the front-channel audio signals areautomatically switched according to an external output channel type.Thus, the volume is optimally set according to the form of areproduction system which incorporates the processor of embodiment 3,and as a result, the SN ratio of the entire reproduction system isautomatically optimized.

In this embodiment, since the output channel type information is input,presence/absence of the virtual surround processing can be controlledaccording to the layout or output format of loudspeakers for rearreproduction.

In the processor of embodiment 3, in the case where, for example, areproduction system which incorporates the audio processor of embodiment3 is constructed, the function of transmitting the position information,i.e., the rear loudspeaker layout information, is added to rearloudspeakers as an interface with the audio processor to automaticallycontrol the presence/absence of the virtual surround processing, theoutput channel type, the volume level, etc. With this, optimumreproduction can be automatically realized.

In the processors of embodiments 1 and 3, the externally-input signalsare front 2-channel signals and rear 2-channel signals, i.e., audio PCMsignals of 4 channels in total, for convenience of illustration.However, the present invention may be applied to an example where theexternally-input signals include a channel for front centerreproduction, a subwoofer channel, or the like, or an example where therear reproduction channel is a monaural channel.

As to the process which is performed based on the output channel typeinformation of the automatic volume controller in the processor ofembodiment 3, an example of switching the presence/absence (ON/OFF) ofvolume control has been described. However, it is also possible that theeffect of the volume control process is variable according to thesetting of the reflection sound processing section or the volumenormalizing section.

Also in the processor of embodiment 3, in the case where theexternally-input audio signals are audio PCM signals of right and leftchannels (2 channels) for front reproduction, pseudo rear-channel audiosignals may be generated in the reflection sound processing section 3600and subjected to the virtual surround processing.

INDUSTRIAL APPLICABILITY

An audio processor according to the present invention possesses theeffect of enabling virtual surround reproduction with smalldeterioration in the SN ratio of an entire reproduction system and isuseful as, for example, an audio processor which realizes multichannelreproduction in a virtual manner only with front loudspeakers placed infront of a listener.

1. An audio processor, comprising an audio processing section forperforming a predetermined sound image localization process on arear-channel audio signal whose sound image position perceived by alistener when reproduced through a loudspeaker placed at the rear of thelistener is at the rear of the listener such that the sound imageposition perceived by the listener when the signal is reproduced througha loudspeaker placed in front of the listener is at the rear of thelistener to generate a sound image localized audio signal, wherein afront-channel audio signal whose sound image position perceived by thelistener when reproduced through the loudspeaker placed in front of thelistener is in front of the listener and the sound image localized audiosignal are output independently of each other.
 2. The audio processor ofclaim 1, further comprising a reflection sound creation section forperforming a reflection sound creation process on an input front-channelaudio signal to generate the rear-channel audio signal.
 3. The audioprocessor of claim 1, further comprising a reflection sound addingsection for adding a reflection sound signal to each of an inputfront-channel audio signal and an input rear-channel audio signal togenerate the front-channel audio signal and the rear-channel audiosignal.
 4. The audio processor of claim 1, further comprising: a volumenormalizing section for controlling the volume level of thefront-channel audio signal and the sound image localized audio signal tobe within a predetermined level range; an adder for adding together thefront-channel audio signal whose volume level has been controlled in thevolume normalizing section and the sound image localized audio signalwhose volume level has been controlled in the volume normalizing sectionto generate a sum audio signal; and a switching section for selectivelyperforming an operation of outputting the front-channel audio signal andthe sound image localized audio signal independently of each other andan operation of outputting the sum audio signal according to a controlsignal indicative of output control information.
 5. The audio processorof claim 4, wherein: the output control information includes outputchannel type information which is indicative of an output channel type;and the switching section performs the switching according to the outputchannel type information.
 6. The audio processor of claim 5, furthercomprising a volume controller for controlling the volume level of anoutput audio signal according to the output channel type information andan input volume level.
 7. The audio processor of claim 4, wherein: theoutput control information includes rear loudspeaker layout informationindicative of whether a layout of a loudspeaker for rear sound imagethrough which an audio signal is output such that a sound image positionperceived by a listener is at the rear of the listener is a layout wherethe loudspeaker is placed in front of the listener, a layout where theloudspeaker is placed at the rear of the listener, or a layout where theloudspeaker is not provided; the audio processing section controlswhether or not to generate the sound image localized audio signalaccording to the layout indicated by the rear loudspeaker layoutinformation; and the switching section selectively performs according tothe rear loudspeaker layout information an operation of outputting thefront-channel audio signal and the sound image localized audio signalindependently of each other, an operation of outputting the sum audiosignal, and an operation of outputting an input audio signal as it is.8. The audio processor of claim 7, further comprising a volumecontroller for controlling the volume level of an output audio signalaccording to the rear loudspeaker layout information and an input volumelevel.